The present invention uses a time-series waveform of biological signal information (dorsal body surface pulse waves) including biological sound and oscillation sampled from the back of a person. The dorsal body surface pulse waves are pressure oscillations generated from the movement of the heart and the aorta, include information related to the systole and diastole of the ventricles, and information related to the elasticity of vascular walls serving as an auxiliary pump for circulation, and are understood as an oscillation system including damping of both viscous damping friction and solid friction. Furthermore, the flow rate (one stroke volume) of blood pumped from the heart varies, and this variation in the flow rate is reflected in the amplitude of the time-series waveform of the dorsal body surface pulse waves. Accordingly, a biological state, particularly a biological state associated with blood pressure, can be apprehended by employing a solution method for calculating the damping ratio of free damping oscillation waveforms, and comparing the amplitudes of prescribed waveform components in one cardiac cycle, preferably two waveform components in an amplification phase.La présente invention utilise une forme d'onde de série temporelle correspondant à des informations relatives à des signaux biologiques (ondes d'impulsion de la surface corporelle dorsale) comprenant des oscillations et des bruits biologiques échantillonnés sur le dos d'une personne. Les ondes d'impulsion de la surface corporelle dorsale correspondent à des oscillations de pression générées par le mouvement du cœur et de l'aorte, comprennent des informations relatives à la systole et à la diastole des ventricules, ainsi que des informations relatives à l'élasticité des parois vasculaires servant de pompe auxiliaire pour la circulation et sont considérées comme un système d'oscillation impliquant un amortissement tant du frottement d'amortissement visqueux que du frottement solide. En outre, le
